Space closure and distalization are important and skill demanding issues in orthodontics. The mechanics for space closure have evolved through many trials and errors. The contemporary space closure mechanisms that are widely practiced are frictionless (or loop) mechanisms and friction (or sliding) mechanisms. In aforesaid contemporary mechanisms, space closing force is applied away from the center of resistance of the segment to be moved; as a result, moments are generated in all three planes of space. Most of those moments that are generated are undesirable in majority of clinical cases.
To control such undesirable moments, very complex biomechanics have been used in the form of loops with pre-activation bends, stabilizing arches, special wires, etc. in frictionless loop mechanisms. In friction (sliding) mechanisms, variable sliding resistance and longer duration to reach working wires for retraction make the techniques statically indeterminate and unpredictable for various movements.
Prior orthodontic literatures have documented power arms (for example in US patent application 20100092905) to control moments generated during orthodontic tooth movement. These are neither capable of controlling the moments in all three planes of space, nor rigid enough to behave exactly as presumed to do so. Such power arms are too bulky to be tolerated by the patients.
The advent of micro-implants, mini-implants and their clinical application in orthodontics has not only extended the envelope of discrepancy, but also simplified complexity of the existing orthodontic appliances by drastically improving end results. Use of micro-implants has definitely reinforced the anchorage and controlled some of the drawbacks of the contemporary retraction mechanisms. However, anchorage loss has been documented in continuous arch wire biomechanics because of the mesial root moments generated on either side of posterior segments in response to the retraction force on anterior segment, which is applied away (occlusal) from the center of resistance of the anterior segment.
In further path of orthodontics evolution, cantilever mechanisms have been advocated where only force is applied between isolated anterior and posterior segments when there is no continuous wire in between. Arch wire itself is extended in a vestibular direction and is terminated at the level of the center of resistance of the segment. As the center of resistance of the anterior segment in the alveolus between lateral incisor and canine root each side is not easily accessible and the rigidity of the vestibular extended wire is questionable, cantilever mechanisms fail to maintain three dimensional controlled space closure.
For last two decades, mini plates like Skeletal Anchorage System (SAS) and mini or micro implants have been used for distal movement of the dentition favoring non extraction mechanotherapy. Though SAS performs well for this objective, better than the mini or micro implants, two additional surgeries performed by oral surgeon and associated costs are the main drawbacks.